As building codes across North America are being modernized in an effort to improve the energy efficiency of new construction, Structural Insulated Panels are more appealing as a means to build with higher R-Values. The dense, closed-cell EPS insulation used in a SIP provides a higher R-Value per inch than traditional fibreglass insulation.
But as a whole, building codes drop the ball when it comes to achieving significant gains in energy efficiency. Fortunately SIPs perform superbly in the very aspects where building codes falter.
To better understand this, we need to step back and understand how heat can be lost or gained. There are six different mechanisms of heat transfer that can come into play in a typical home:
Conduction - the transfer of heat within an object or between two objects that are in contact. A pot gets its heat from contact with the stove element.
Convection - the transfer of heat that occurs when a liquid or gas comes into contact with a material of a different temperature and distributes heat accordingly. Hot air rises since it is less dense than cold air, moving heat upward, while cold air falls.
Radiation - the transfer of heat by means of electro-magnetic waves. The Earth gets its heat from the Sun exclusively via radiation, because the void of space in between the two prevents both conduction and convection.
Conduction, convection and radiation are the three primary scientific mechanisms of heat transfer. But there are also three secondary mechanisms at play in building science.
Infiltration – the transfer of heat when air pressure differences between the exterior and interior force air to infiltrate a building. A strong wind will often “push” unconditioned exterior air inside a building.
Air intrusion – when exterior air infiltrates a wall cavity but doesn’t continue into the building, exiting back to the outside instead. While there is no draft felt inside, the thermal patterns inside the wall insulation are affected.
Moisture Accumulation - when moisture permeates an insulation material, it will reduce the insulation’s effectiveness, contributing to heat loss/gain.
Out of these six different mechanisms that affect a building’s ability to preserve heat in the winter and conditioned air in the summer, building codes only address the first: conduction. Building codes have tunnel vision when it comes to energy efficiency, focusing on minimum R-Values for insulation materials used throughout a house. This is known as a “prescriptive” approach. As long as a builder conforms to prescriptive standards, the building complies with code.
The problem is that R-Values are determined in a laboratory setting by measuring how much heat moves through the insulation via conduction. Nowhere do building codes set quantitative standards to tackle the other mechanisms of heat transfer. Moreover, the emphasis on the R-Value of an individual building component (i.e. insulation), overrides what’s truly important for lowering energy bills: actual system-wide performance. It’s only with an accurate understanding (and measurement) of wall, roof or foundation assemblies that a system be properly designed for energy performance.
When it comes to highlighting the huge discrepancy between building codes and true performance, certain research studies stand out, notably the U.S. Department of Energy’s Oak Ridge National Laboratory’s (ONRL) groundbreaking analysis of attic insulation. Using a full-scale attic test module built to residential home standards and exposed to typical exterior conditions, the study accurately measured the thermal performance of a conventional roof system.
The conclusions were shocking. The ONRL determined that the thermal resistance of loose-fill fiberglass insulation is as much as cut in half when the outside temperature is -28°C. Specifically, insulation rated at R-22 performed at a mere R-9 level. Researchers identified distinct natural convective forces at play within the fiberglass insulation itself as a major source of heat loss. This result highlights the flaw with building codes, which are based on conductive heat loss only.
Another very revealing study was conducted by Brock University researchers, who had the opportunity to analyze temperature variances within the exterior walls of two nearly identical houses – one using traditional R-19 fiberglass insulation and the other built with SIPs that featured an R-17 foam-based EPS insulation.
The study found that the R-17 EPS outperformed the R-19 fiberglass hands down, and highlighted a number of interesting findings:
• The R-19 fiberglass insulation performed at an equivalent R-4 level when the outdoor temperature was -10.5ºC (13.1ºF).
• The SIP wall house with R-17 EPS insulation maintained its true R-value throughout the duration of the 1 year study.
• The R-17 EPS SIP wall house used 33% less energy than the R-19 fiberglass wall house.
The Brock University study clearly demonstrates that other mechanisms besides thermal conduction are at play in a real world setting. Otherwise the two homes would experience similar energy usage. It also shows that “building to code” doesn’t necessary result in an energy efficient home, because of code’s overriding focus on prescriptive R-values.
Some observers point out that building codes are moving beyond just R-values. Many jurisdictions in North America have amended their building codes to require homes to meet certain levels of energy efficiency set by major energy rating programs, like Energy Star and EnerGuide. Ontario and British Columbia, for example, require new homes to obtain an EnerGuide 80 rating. The “80” can be translated to an actual measure of energy usage, so this can be seen as a full system approach – moving beyond the R-Value of insulation components, and therefore beyond just thermal conduction as the only source of energy loss in a house.
Unfortunately these recent code initiatives have not had this desired result, for a couple important reasons:
• Codes still have a “prescriptive path”, allowing a builder to bypass the need to obtain a formal EnerGuide rating. The overwhelming majority of builders continue to build according to code’s minimum R-value requirements.
• In the rare instance where a builder truly builds to EnerGuide 80 performance, the problem is that the rating itself is determined by energy modelling software where the user inputs insulation R-Values, but has no opportunity to specify the type of insulation. Essentially, thermal conduction dictates the calculation.
So while building codes don’t reflect five of the six mechanisms of heat transfer, new home buyers can still take steps to address energy loss from non-conductive forces. One of the most effective ways is to build with non-traditional insulation materials, particularly SIPs. SIPs can be used as the structure and insulation for entire wall, foundation, roof and floor systems. The key to SIPs is that there is no wall cavity. The EPS insulation is rigid and solid, unlike the porous nature of traditional fiberglass.
Consequently, SIPs can truly claim to eliminate thermal transfer from the other five mechanisms. There is no convective loop, air infiltration or air intrusion, because SIPs are a true air barrier – the solid insulation prevents air from circulating. Likewise there is no thermal transfer resulting from moisture accumulation, as SIPs are a vapour barrier as well. Finally, radiative heat transfer, which occurs in the void of space, is negligible. While in theory heat can transfer by radiation within a cell in the insulation, its adjoining cell walls are essentially at the same temperature anyway.
These properties explain why SIPs are vastly superior to traditional fiberglass insulation. While the two materials share similar characteristics for resisting conductive heat transfer (although measured inch per inch, SIPs boast a higher R-Value), SIPs do not face the other five mechanisms.
The proof is in the performance. The Brock University finding that SIPs use 33% less energy than its fiberglass counterpart is typical of the experience of SIP home owners. And this study only involved SIPs as the exterior wall. Homes that also use panels in their foundation and roof systems typically benefit from energy savings of 50% and more.
It’s this proven performance that separates SIP homes from traditional fiberglass insulated homes built to building code minimums. As a home buyer, if you insist on energy efficiency in your new house then SIPs are the ideal choice. Not only are they extremely effective in delivering high Energy Star and EnerGuide ratings, they are clearly superior where it counts the most: lowering your monthly energy bills.